Manufacture of crude rubber



Patented Oct. 8, 1935 UNITED STATES PATENT OFFICE John McGavack, Leonia,N. J assignor, by mesne assignments, to General Rubber Company, NewYork, N. Y., a corporation of New Jersey No Drawing. Application October3, 1931, Serial No. 566,801

12 Claims.

This invention relates to the manufacture of new rubber products fromlatex and particularly from such as that known as Hevea brasiliensis.

This case is a continuation in part of case Serial No. 495,303, filedNov. 12, 1930.

Crude rubbers have been generally obtained by coagulating whole orconcentrated latices with acids or otherwise, or by drying the latex byspray drying or otherwise, and recovering the crude rubber. Theserubbers have been used for the manufacture of various rubber goods. Thephysical properties of these rubbers, and the properties imparted to thevulcanized rubber goods containing such rubbers, have been capable ofcertain variations, the extent of such variations being limited by thefixed natural content of nonrubber constituents present in the latex. Inno instance can these rubbers contain more than the naturally-occurringproportions of the non-rubber constituents of the latex. In the case ofthe usual acid-coagulation processes, the resulting rubbers contain lessthan the total protein content of the original latex, and only minorproportions of the other water-solubles present in the latex.Furthermore, the proteins contained in such coagulated rubbers havethemselves been coagulated, and hence have been denatured.

It has been proposed to evaporate all of the water from latex byspray-drying, the products of such a process being the so-calledwhole-latex rubbers, containing all of the non-rubber constituents ofthe latex in their natural fixed proportions relative to the caoutchouccontent. Another proposal has been to separate latex into two layers bycreaming or centrifuging and to recover a crude rubber from the heavierlayer or serum by acid coagulation. Such a crude rubber containscoagulated, and hence denatured, proteins in higher proportions thandoes an ordinary rubber obtained from the same original latex by theusual processes of coagulation, while the content of water-solublesremains substantially unchanged. Such crude rubbers are known to beinferior for commercial purposes. It has also been proposed to mix withordinary rubber the evaporation residue of the serum resulting from thecoagulation of rubber latex. Such serum, and the evaporation residuetherefrom, are high in water-solubles, both organic and inorganic, butare very low in proteins, containing only a small amount of residualuncoagulable albumens.

An object of this invention is to provide a method of controllablyincreasing the content 5 of the non-rubber latex solids in crude rubberby controlling the ratio of non-rubber latex solids to the caoutchouccontent of a given portion of latex that is to be evaporated, Anotherobject is to produce rubber products, having highly desirable physicalproperties such as high tensile, 5 non-tearing, and high resistance toageing, from crude rubber regulated in content as to its nonrubber latexsolids. Other objects will be apparent from the following detaileddescription.

The invention broadly. comprises separating 10 latex preserved in anysuitabie manner against coagulation, into an upper layer containing apercentage of rubber greater than that originally present and a lowerlayer containing a sub-original percentage of rubber and then recovering15 the lower layer and evaporating it, as by spray drying, to form acrude rubber. The separation into two layers may be carried out by acreaming operation with any of the known creaming agents such asalginates, pectin, pectin bodies, Irish 20 moss, Karaya gum or similarsubstances,or by a centrifuging process in which case creaming agentsmay or may not be used to assist the separation. In the creamingprocess, the ratio of rubber to non-rubber solids in the lower layer 2will depend on the amount of creaming agent used and the time allowedfor creaming. This can be regulated as desired. In the centrifugingprocess the ratio desired may be regulated by varying the size of theopening for the heavy and 30 less heavy liquids as they exit from themachine or by varying the rate of flow through the machine or both.

Thecreaming process is preferred as it is subject to less varyinginfluences. Where only a 35 very small amount of creaming agent isemployed the composition of the lower layer is very similar to thecomposition of the upper layer. However, as the amount of creaming agentis increased the difference between the two layers becomes very marked;in fact the ratio of rub-- ber to non-rubber in the lower layer becomesgradually smaller and by repeatedly increasing the amount of creamingagent the ratio will approach Zero, while the proportions of the variousnonrubber solids relative to each other remain substantially unchanged.This enables one to obtain a composition of matter which has any desiredratio of the non-rubber constituents found in latex to rubber. The nextstep is to obtain in a 50 solid state the entire solids content of thelower layer by evaporation. This may be done by spray drying, or by anyother method of drying which is adapted to give complete recover of thesolids content of the liquid. The composition of matter obtained by thisprocess is a crude rubber in which the ratio of total non-rubberconstituents to rubber may have any desired value greater than that inthe original latex, and in which the proportions of all of the solidnon-rubber constituents relative to each other are substantially thesame as in the original latex. Because of the absence of any stronglyacid or alkaline conditions and of any prolonged heat treatment in anystage of the entire process, the product is further characterized inthat the proteins contained therein are present in an undenatured state.To this fact are due in large measure the valuable physical propertiesof the product and of the vulcanized rubber goods made therefrom.

Rubbers obtained by this method have certain peculiar advantages. Amongthese is a cured rubber which has the same tensile as a firstgraderubber but has a considerably reduced stretch. Another one of theadvantages is due to the faster curing powers of such a rubber. Afurther advantage of this rubber due to the high content of undenaturedproteins, manifests itself in. nontearing properties, making it usefulfor inner tube construction, footwear, and such similar products. Rubbershoe tops made of such a rubber are particularly resistant to tearingwhen the shoe is pulled on, and the heel pieces are made more rigid inconstruction by employing such a rubber. The new rubber is also found tobe particularly resistant to rubber solvents, and such a rubber isuseful in the manufacture of hose, gloves, etc. for handling varioussolvents.

By this invention the resulting crude rubber can be made to contain fromabout 12% to 80% by Weight of the non-rubber latex solids insubstantially the same proportions relative to each other in which theyoccur in the latex, and correspondingly, from about 88% to 20% of rubberas caoutchouc.

The following examples are illustrative of the invention but are not tobe construed as limiting thereof.

Example 1.-To 1000 lbs. of ammonia preserved latex having a total solidsconcentration of 36%, 50 lbs. of a 1% ammonium alginate solution areadded. The mixture is allowed to stand for 24 to 48 hours. A separationinto two layers occurs. The lower layer is separated and moistureremoved by spray drying.

The composition of the crude rubber thus obtained is shown in thefollowing table, together with that of the original latex from which itwas derived and that of the usual whole-latex rubber derived therefrom:

The'composition given for the original latex is typical of latices fromHevea brasz'lienszs. It is evident that the proportions of thenon-rubber constituents in the new rubber relative to each other aresubstantially equal to those in the original latex; Similar relationshold when. other latices of similar composition are employed in theproduction of crude rubbers by the process oi! this invention.

The new rubber described in'the above example, when vulcanized, showedextremely valuable non-tearing properties, was faster curing, 5

had good tensile, and was more resistant to ordinary rubber solvent.When this rubber was compounded and vulcanized in a first grade tubeformula and compared witha similar compound using pale crepe there wereobtained the 10 following results:

Permeability is expressed as cos. of air (at C. and l atmospherepressure) per hour per sq. in. area per inch thickness per atmospherehead at 40 0.

Emample 2.--To indicate the properties of finished vulcanized productsembodying a series of crude rubbers of this invention having varyingproportions of non-rubber latex solids, as compared with a product usinginstead a well known crude rubber, pale crepe, the following table sgiven. The formula employed comprises (parts by weight) l Parts 5 Cruderubber 100 3 Zinc oxide 10 Blanc fixe 17 Lithopone 12 Mineral wax 1Stearic acidu' V 4 40 Sulphur 2 Antioxidant 1 Accelerator 1.25

Composition of crude A B C D 7 F rubber Percent latex non-rubberconstituents 8 25 29 34 38 Percent rubber as caout- 50 chouc 92 75 71 6662 50 Physical properties of vulcanized product Tear (lbs.)' 19 25Permeability .0009 .0006 Tensile (lbs/sq. in.) 3500 3200 Tensile afterageing 8 hrs. at 249 F. at 100 percent elongation (in air) 300 900 800910 970 1100 The rubber used in A was ordinary pale crepe; in the othernlillxes were used the new'crude rubbers of varying compositions as 0 sown.

This table shows clearly how increasing the ratio of the non-rubberlatex solids to rubber over a wide range produces vulcanized productshaving exceptionally high tear resistance, better ageing and lowerpermeability.

In addition to these characteristics and results it has also been foundthat by the addition of fillers to this type of rubber the tearresistance, instead of being decreased, is actually improved; in fact byincreasing the volume of filler to three times its original volume thetear resistance has been doubled. This is entirely contrary toresultsobtained with any known crude rubber now on themarket.

Another advantage possessed by this type of rubber is that when it iscompounded for example with carbon black in a tread stock, it will givea very hard tread, much harder than any other type of rubber in the samecompound has ever been known to give.

It is clear that the invention can be practiced in various forms, forinstance any desired ratio of the non-rubber latex-solids to rubber maybe obtained in a single composition by the proper blending of variousrubbers prepared as indicated herein, or the new rubbers may be added inany proportions to a rubber composition containing ordinary crude rubberto raise the proportion of non-rubber latex-solids therein as desired;for example if one desires a rubber product having the properties of arubber such as C in the above table, this may be obtained by propercontrol of the creaming operation or a rubber such as E may be blendedin the proper proportions with a normal rubber or other rubbercontaining a lesser proportion of non-rubber latex solids.

It is to be understood that while latex from Hevea brasiliensis has beenused for the purpose of illustrating the invention, latices containingproportions of solid non-rubber constituents approximately similar tothose of Hevea brasiliensis, are to be considered as equivalents ofHevea brasiliensis. within the scope of the appended claims.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A vulcanized inner tube resulting from the vulcanization of a rubbermix containing a crude rubber derived from Hevea brasiliensis latex,said crude rubber consisting of from about 12% to about 50% of thenon-rubber latex-solids and from about 88% to about 50% caoutchouc, saidtube having a tearing strength greater than 5 lbs. and a permeability toair less than .0017.

2. A vulcanized inner tube resulting from the vulcanization of a rubbermix containing a crude rubber derived from Hevea brasiliensis latex,said crude rubber consisting of from about 12% to about 50% of thenon-rubber latex-solids and from about 88% to about 50% caoutchouc, theproportions of said non-rubber solids relative to each other beingsubstantially equal to those characteristic of the normal latex, saidtube having a tearing strength greater than 5 lbs. and a permeability toair less than .0017.

3. A vulcanized inner tube resulting from the vulcanization of a rubbermix containing a crude rubber derived from Heoea brasiliensis latex,said crude rubber consisting of from about 25% -to about 50% of thenon-rubber latex solids and a chemical creaming agent, recovering thedenser 5 of said portions, said denser portion being relatively poor inrubber content, and removing water from said denser portion.

5. A process as described in claim 4 wherein the water is removed byspray drying the denser portion in such a manner that the proteins areprevented from being denatured.

6. A rubber composition of improved durability embodying a mixture ofordinary rubber and the evaporation residue of a rubber-containinglatex- 16 serum which residue is characterized in that it containssubstantially all the latex-nonrubber solid constituents in an amount atleast equal to one-third of the weight of the caoutchouc of the residue.20

7. A rubber composition of improved durability embodying a mixture ofordinary rubber and the evaporation residue of a rubber-containinglatexserum which residue is characterized in that it containssubstantially all the latex-no-nrubber solid constituents in an amountsubstantially equal to the weight of the caoutchouc of the residue.

8. A process of producing vulcanized rubber goods of improved durabilitywhich comprises vulcanizing a rubber mix containing ordinary rubbercompounded with the evaporation residue of a rubber-containinglatex-serum which residue is characterized in that it containssubstantially all the latex-nonrubber solid constituents in an amount atleast equal to one-third of the weight of the caoutchouc of the residue.

9. A process of producing vulcanized rubber goods of improved durabilitywhich comprises vulcanizing a rubber containing ordinary rubbercompounded with the evaporation residue of a rubber-containinglatex-serum which residue is characterizedin that it containssubstantially all the latex-nonrubber solid constituents in an amountsubstantially equal to the weight of the caoutchouc of the residue.

10. A vulcanized rubber product of improved durability resulting fromthe process set forth in claim 8.

11. A vulcanized rubber product of improved durability resulting fromthe process set forth in claim 9.

12. As a new product a rubber-containing latexserum evaporation residuecharacterized in that 5 it contains substantially all thelatex-nonrubber 5 solid constituents in an amount at least equal toabout one-half of the weight of the caoutchouc of the residue.

JOHN MCGAVACK. w

